The invention relates to a process for the chemical plotting of boundary layer flows on anodically oxidized uncompacted aluminum surfaces.
For many areas of technology, observation of boundary layer flows is important. In particular, it is of interest to determine boundary layer flows in machine, apparatus and equipment parts as well as in cooling and heating units, along walls of ships, marine structures, liquid tanks, and the like. Flow phenomena and their determination also give information concerning the boundary layer thickness and concerning heat and material transfer. Methods used to this end, employing measuring probes, e.g. laser anemometers, by attaching a plurality of wool threads and photographing them during exposure to flow; by erosion or entrainment of soluble or viscous coatings; by chemical alteration of surface layers or surface coatings by means of suitable chemicals introduced into the flowing liquid, e.g. the schlieren method are very expensive.
It is further known to plot boundary layer flows in gases by exposing an anodically oxidized uncompacted aluminum surface to an air stream mixed with reactive acid or basic chemical reagents and coloring the layer which is differently altered by the gas stream (U.S. Pat. No. 3,890,835).